1. Field of the Invention
The present invention relates to an improved method of terminating a wire wound noise preventing resistance cable, which is used in the ignition system for an automotive engine, after the cable has been cut and stripped of an outer insulating cover at an end thereof.
2. Statement of the Prior Art
Generally, there are two types of method of terminating a wire wound noise preventing resistance cable. One method is referred to as a "contact pin type" method in which an electrical connection between a solderless terminal and a resistance wire is attained via a contact pin disposed at the end of the resistance wire. The other method is referred to as a "folding type" method in which a direct electrical connection between the terminal and the resistance wire is attained by removing an outer insulating cover from the end of the cable to expose a wire wound core therein and folding back the exposed wire wound core over the cable. The "contact pin type" method consumes labor in disposing a pin at the end of the resistance wire, and a superior electrical connection can be attained with the "folding type" method. Thus, the latter terminating method has been used more frequently. For example, the folding and connecting structure of a strand type resistance wire is disclosed in U.S. Pat. Nos. 3,787,800 and 3,266,008.
However, in a case where the "folding type" method is used for terminating a wire wound type resistance cable, the resistance wire easily unravels when the end portion of the wire is stripped of the outer insulating cover, thereby causing leakage problems.
In addition, it is known that a magnetic substance is included in the core of the cable of this type so as to improve the noise preventing capability. However, there is a drawback in that if a great quantity of such a magnetic substance is included in the core, the tensile strength and extensibility of the core is deteriorated, and cracks are generated during the terminating operation when the leading end of the wire wound core is folded back over the cable, the resistance wire being thereby broken.
A general connecting structure for the end portion of a wire wound noise preventing resistance cable is disclosed in U.S. Pat. No. 3,518,606, but there is no disclosure there in with regard to a method of preventing such unraveling of the resistance wire.
In order to solve the above drawbacks, the development of a new resistance cable has been desired in which the resistance wire is prevented from unraveling when removing the outer insulating cover from the end thereof, and in which the core has good mechanical properties, such as a high tensile strength and so forth.
The inventor of the present invention discloses a method of manufacturing a resistance cable in which a resistance wire can be wound around a core in compact fashion at a uniform pitch, and in which the resistance wire is prevented from unraveling, in the official gazette of Japanese Patent Public Disclosure No. 16891/1988.
In the cable manufactured in accordance with the method disclosed in the above official gazette, since the core is made from a fluorine rubber compound by extruding the same in an unvulcanized state, and since a resistance wire is wound around the core so made, the resistance wire is partly embedded in the surface of the core. Due to this construction, with the resistance cable disclosed in the official gazette, even when extruding from an insulating cover, as well as when removing the insulating cover from the end of the resistance cable, the resistance wire that is wound around the core in a compact fashion is prevented from being displaced and/or unraveling. In addition, although fluorine rubber is a compound that contains a great quantity of magnetic substance, it remains superior with regard to its tensile strength, extensibility and so forth, even after it has been vulcanized, and thus the core is made free from the above-mentioned cracking problem.
However, although it is possible to solve the unraveling problem arising at the time of removing the outer insulating cover, it often happens that during a cable-terminating operation after the removal of the outer insulating cover, particularly when a solderless terminal is manually press fitted over the end of the cable, that the hand of a worker touches the exposed wire wound core, thereby often causing the leading end of the resistance wire to unravel. With a view to solving the above-mentioned problem, an adhesive is conventionally applied to the leading end of the wire wound core that is exposed when removing the outer insulating cover so as to prevent unraveling.
However, with this method in which an adhesive is applied to the wire wound core, there are drawbacks in that the application of the adhesive to the wire wound core takes time and in that electrical connection errors between the terminal and the resistance wire are caused due to the application of adhesive to the portions which require no adhesive, thus making the quality of a product unstable.